Method for manufacturing planar raised cathode gas tubes

ABSTRACT

A method for fabricating segmented planar raised cathode elements in an alphanumeric display gas tube employing a weld and de-weld process.

United States Patent Armstrong [4 1 May 30, 1972 [54] METHOD FORMANUFACTURING PLANAR RAISED CATHODE GAS TUBES [72] Inventor:

[73] Assignee: Sperry Rand Corporation 221 Filed: Jan. 23, 1970 [21]App1.No.: 5,436

James B. Armstrong, Phoenix, Ariz.

52 us. CI ..219 117, 219/78 51 Int. Cl ..B23k 9/00 [58] Field ofSearch..2l9/9l, 78, l 17; 29/625 [56] Reference Clted UNITED STATES PATENTS2,399,753 5/1946 McLam ..2l9/78 Primary Examiner-J. V. Truhe AssistantExaminer-Hugh D. J aeger Attorney-S. C. Yeaton 57 ABSTRACT A method forfabricating segmented planar raised 'cathode elements in an alphanumericdisplay gas tube employing a weld and de-weld process.

2 Claims, 11 Drawing Figures Patented May 30, 1972 3,666,911

4 Sheets-Sheet l FlG .lc.

'r/vvlf/vral? JAMES B. ARMSTRONG ATTORNEY Patented May 30, 19723,666,911

4 Sheets-Sheet 2 IW VE/VTOR JAMES 5. ARMSTRONG A 7'TOR/VEY Patented May30, 1972 3,666,911

4 Sheets-Sheet :5

I/VVENTOIP JA M55 5 A HMS THO/V6 B) ATTORNEY WELDER Patented May 30,1972 4 Sheets-Sheet 44 IN l/E/V TOR (/4 M53 5. 4 EMS THO/V6 ATTORNEYFIG.4.

BACKGROUND OF THE INVENTION 1. Cross References This invention relatesto a method for fabricating planar raised cathode, alphanumericindicators of the gas discharge type, such as disclosed in theco-pending patent application, Planar Raised Cathode Alpha-Numeric GasDischarge Indicator, Ser. No. 742,662, filed July 5, I968, assigned tothe same assignee as the present invention.

2. Description of the Prior Art 7 The assembly of a gas tube requirestwo flat glass plates (an anode and cathode plate), a spacer betweenthese two plates, and a fill tube..These four parts are sealed togetherto form a hermetic envelope. The envelope is then evacuated, back filledwith ionizable gas such as neon, and sealed. In order to obtain therequired display information, dc power is applied between thetransparent electrode on the anode plate and a predetermined array ofsegments on the cathode plate. The application of power between opposingelectrodes causes the gas between them to ionize and visibly form thedesired number or letter. 7

Previously, the construction of planar segmented cathodes foralpha-numeric gas tubes has revolved, with a limited periphery, aroundthe basic method of vacuum depositing segmented cathodes on a flatglass'plate. The vacuum deposited type of numeric gas tube suffers fromserious operational limitations as lowresistance paths build up betweenthe segmented cathodes. To overcome this problem, 7 channels betweeneach segment have been implemented. The channeling technique hasdefinite requirements in terms of width, depth, and a sharp edge. Such acombination is very delicate and difficult to achieve without error andconsequently has a high discard rate. In addition, glass breakoutbetween the channel and feed-through pin becomes a problem in lappingand polishing the cathode plates.

SUMMARY OF THE INVENTION The method of the instant invention is directedto the fabrication of the planar raised cathode plates and provides aconvenient and expeditious process for attaching the cathode elements toelectrical connections (pins). The method may comprise the followingdiscrete steps. A sheet in the form of a blank is processed to delineatethe outline of the elements with the exception of connecting tabs. ,Theresulting sheet is stencil-like in that material in the shape of shortchannels between the elements and the sheet is removed, but the desiredelements remain. In a separate step, the central portions of pins areimbedded in a glass substrate such that the extremities of the pinsextend therefrom. The above two assemblies are then juxtaposed in such amanner that each pin is adjacent to an element. After the positioning,the elements are welded to their respective pins. An electrical currentis passed through each element and the still attached sheet and discardpieces to separate the elements. The path of this current mustnecessarily be through one or more of the tabs, and because of theirrelative high resistance, will generate suflicient heat to burn them off(referred to as the de-weld process). Thusly, the elements are separatedfrom the sheet and the other discard pieces. The segmented raised planarcathode element assembly is now ready to be combined with the spacer,plate and the fill tube.

A primary object of this invention is to provide a simple andinexpensive method for positioning and aligning the cathodes during thebase assembly of gas tube fabrication.

Another object of the invention is to provide a method for positioningand aligning in-plane anode and cathode elements.

Another object of the invention is to provide a method particularlysuitable to mass production techniques Another object of the inventionis to provide predictable operating parameters.

Another object of the invention is to provide ultra-long theoreticaluseful life of the resulting display device.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates the structure ofthe stencil-like cathode sheet prior to welding the elements to theconnector pins.

FIG. la illustrates the trapezoid shaped connections between theelements and the waste material.

FIG. lb illustrates another embodiment of the connections between theelements and the waste material.

FIG. 1c illustrates another embodiment of the connections between theelements and the waste material where the thickness of the connectionhas been reduced.

FIG. 1d illustrates a method for implementing the instant invention toposition the anode contact on a pin in the cathode substrate.

FIG. 2 is an exploded view of the components of the complete planaralphanumeric raised cathode gas discharge tube.

FIG. 2a is a perspective view of the tube base.

FIG. 3 illustrates a method for welding and de-welding.

FIG. 4 illustrates a method for using various jigs and plates toimplement the instant invention on a mass production basis.

FIG. 4a illustrates a configuration of the electrodes for the weld andde-weld process. I

DETAILED DESCRIPTION OF THE INVENTION In FIG. 1 there is shown achemically treated plate 1' having a nominal thickness of 0.005 inchesand chemically processed or otherwise fabricated to obtain an outline ofparts as shown. The processed sheet is similar to a stencil in generalconfiguration. However, instead of the desired figures being'removed asin a stencil, the material representing intermittent channels formingthe outline of the desired figures is removed.

The elements are processed from sheet 1 but remain connected thereto byat least one point of connection and may be processed by any number ofwell known processes, such as stamping, etching, cutting by laser,ultrasonic means, electroforming, or electrical discharge machining.Presently, satisfactory results in terms of cost and accuracy have beenobtained by etching. The process is two-fold in that first one side isetched until half the depth of the material to be removed is removed.Secondly etching is completed from the other side, but this time thefusible tabs are subjected to the etching process. The advantagesobtained are that the fragile tabs are not very susceptible tounintentional breakage and that the thickness of the tabs can be reducedto any desired size.

The desired elements 6 remain joined to the surrounding sheet I bytrapezoidal or triangular connections 4 and to the inside orcircumscribed portions 2, 3 of the sheet by similar connections 5. Theconnections 4 and 5 may have any of the suggested configurations in FIG.1a and FIG. lb or variations thereof. The only requisite of theconfiguration is that it have sufficiently narrow cross section toprovide a high resistance path to a current passed through it. A furthervariation is shown in FIG. 10 and illustrates that the cross section maybe further reduced by having the connections 4 and 5 thinner than theadjacent sheet 1, 2, 3, and element 6. The orientation and size of theelements 6, processed in sheet 1 may be of any configuration and dependonly upon the nature of the characters desired.

Sheet 1 may, in addition, contain a representation of a decimal point asindicated by element 6 The principle is the same as for elements 6 inthat element 6' is connected to sheet 1 by fusible tabs 4 and is weldedat its approximate center to pin 8' (FIG. 3). Similarly, element 6" maybe formed from sheet 1, but connected thereto by fusible elements 4.Element 6" may also have small indentations on either side as indicatedin FIG. 1 to facilitate bending of the outermost parts after welding sothat the raised ends made contact with anode l 1 (FIG. 2). Otherconfigurations may also be used to obtain a pressure contact with anodel 1.

Referring to FIG. 2a, the glass substrate 9 is apertured to receive anumber of electrical connecting pins 8 which are hermetically sealed tosubstrate 9. The ends of pins 8 on the upper side of substrate 9 extenda predetermined distance;

good results are obtained with a distance of about 0.005 inches. Thepins extend below the substrate 9 bottom surface a convenient distancesuitable for connection with a mating receptable or other electricalattachment. A preferred method of manufacturing the substrate 9 and pins8 (and 8, 8"), assembly may be that of having the pins sealed in thesubstrate as previously discussed with the pins 8 (and 8', 8") initiallymounted flush with the upper surface of substrate 9. The side of thesubstrate having the flush pin terminations is then etched away so as toexpose the desired length of each pin above the etched substratesurface. During etching, a cup shaped indentation or moat 7" is formedin the substrate around the base of each pin. The moats formed duringthe substrate etching process result from the use of a substrate-pincombination which produces compressively strained seals; these strainedglass seal areas etch more rapidly than the unstrained portions of thesubstrate. The advantage of the latter method is that of an increasedoperational life as a low resistance path between pins formed bysputtered products is inhibited. Further details of the sputteredproducts effects are discussed in pending application entitled PlanarRaised Cathode Alpha-Numeric Gas Discharge Indicator," Ser. No. 742,662,filed July 5, 1968.

The heart of the present invention is the manufacturing process forcombining the sheet 1 and substrate 9 to form the cathode assemblyshown. The presently known best mode of joining the elements to the pinsis that of electrical welding. However, it is anticipated that othermeans for accomplishing the bond may be employed if circumstancesindicate that another method is preferable. In FIG. 3 the stamped sheet1 is aligned by registration means 28 and 29 with the substrate 9 andpin 8 assembly so that each of the pins 8 will contact one of theelements 6. For purposes of explaining the invention, only element 6 andpin 8 will be discussed, and it is understood that the discussion isalso true for elements 6', 6" and 8', 8". The number of pins 8 persegment 6 is dictated, not by electrical requirements of function of thegas tube, but by the mechanical rigidity required. After alignment, alower or first electrode 27 of a welding current source 14 is attachedto a pin 8 and an upper, or second, electrode 23 is placed on theassociated segment 6 in proximity to the pin 8 under the element 6.Slight pressure is applied to the upper electrode to insure physicalcontact between the element 6 and pin 8. Current of a predeterminedmagnitude and for a predetennined time flows between the electrodescausing the pin 8 to become welded to the element 6. This process isrepeated for each pin/segment combination. Sheet 1 may also have arectangular hole with its center approximately in alignment with pin 8"and after welding elements 6 and 6 but before de-welding, a triangularor a V-shaped element 13 (see FIG. 2) may be positioned in the hole (seeFIG. 1d) the latters outline being used as a positioning guide, andwelding the triangular or V-shaped element to pin 8 To separate theelements 6 from sheet 1 and waste material 2 and 3, a method ofde-welding is used. The trapezoidal-like shaped connections 4 and 5,referred to hereinafter as tabs, are of relatively small cross section.As such, they constitute a high resistance path to an applied current.Any current passed through the tabs will cause a heat buildup and if thecurrent is large enough, the generated heat will melt the tabs. Theburnoff process is accomplished by attaching an electrode 23 of thecurrent source 14 to an element 6 and a second electrode 27 is connectedto either the waste material 2 or 3 or sheet 1. A current will then flowfrom the first electrode 23 through the element 6, through one or moreof the tabs 4 and 5 joining the tab to either of waste material 2 or 3,or sheet 1, and thence to the second electrode 27. The current willcontinue to flow until the heat buildup in the tab or tabs is sufficientto melt the tab or tabs. When the tabs melt, the current path is an opencircuit indicating that the connection between the element 6 and thewaste material 2 or 3 or sheet 1 is severed. This process can berepeated for each of the elements until each is free of surroundingmaterial. The de-weld operation may be enhanced if sheet 1 is slightlyraised above the pins. After welding, there will be a slight tension onthe tabs which will provide a positive severing force on the tabs. Thesize and duration of the current for both the weld and de-weld processesmay not be of such magnitude as to cause damage to the glass substrate9. An advantage of this method is that of speed and it also tests theweld 7 for a good electrical and physical contact.

Referring to FIG. 4 and 4a, there is illustrated apparatus suitable forimplementing the instant invention on a mass production basis. The glasssubstrate 9 with embedded pins 8, 8' and 8" (cooperating with elements6, 6' and 6" or 13, respectively) is placed in a jig 26. Jig 26 isadapted to hold glass substrate 9 securely and is sufficiently thin toallow pins 8, 8' and 8" to extend therethrough. The jig 26 has two ormore alignment rods 28 extending from both sides. Base 27 is slidablyadapted by means of alignment holes 29 to receive the bottom of rods 28of jig 26 and contains holes 23', 24' and 25' positioned to receive andmake a good electrical contact with pins 8, 8 and 8". Base 27 isconnected to an electrode 16 the current source 14 (the negativeterminal being shown). For ease in orienting the elements 6 to the pins8, sheet 1 has one or more alignment holes 29 which cooperate with rodor rods 28. Plate 20 is of electrically conducting material and hasconnected thereto a plurality of electrodes 23 (see FIG. 4a) so arrangedthat each corresponds to one of elements 6 and is in general alignmentwith pins 8; similarly, electrodes 24 and 25 are connected to plate 20to cooperate with elements 6' and 6" and are aligned with pins 8' and8", respectively. Pins 22 are connected to plate 20 but electricallyinsulated therefrom by material 21. One of pins 22 cooperates and is ingeneral alignment with waste material 2, and the other cooperates and isin general alignment with waste material 3. There is connected to eachof pins 22 an electrical lead 19'. Plate 20 contains one or morealignment holes 29 which cooperate with rod or rods 28. The weldingcurrent source 14 may be any suitable welder wherein the magnitude andduration of the welding current can be controlled- One electrode of thewelder is connected to base 27 and the second electrode to the commonpole of single pole double throw switch 15. One output of switch 15 isconnected to plate 20 by lead 18 and the other output to sheet 1 by lead19 and pins 22 by lead 19'.

In operation, the glass substrate 9 is placed in jig 26. The jig is thenplaced on base 27 with the registration means (28 and 29) aligned andpins 8, 8 and 8" inserted in their respective holes 23', 24 and 25.Next, sheet 1 is slidably placed on top of jig 26 by using registrationmeans 28 and 29. Finally, plate 20 is placed over sheet 1 with holes 29of the plate aligned with rod 28. The pins 22, 23 and 24 and 25 willthen be in contact with and at the approximate centers of elements 2 and3, 6, 6' and 6" respectively. In the weld operation, the switch 15 ispositioned to connect line 17 with line 18. The current path is thenestablished through base 27, pins 8, 8 and 8", elements 6, 6 and 6",pins 23, 24 and 25 and plate 20. In the deweld operation the currentpath is through the pins 8, 8' and 8", elements 6, 6' and 6", tab 4sheet 1 and lead 19 to switch 15 and through pins 8, 8' and 8" elements6, 6' and 6", tabs 5, waste material 2 and 3, pins 22 and lead 19' toswitch 15. The current passing through elements 6, 6' and 6" to thesheet 1 and to waste material 2 and 3 is of sufficient magnitude tocause burn-ofi of fusible tabs 4 and 5. The current will flow until alltabs 4 and 5 are melted and create an open circuit. Some means may berequired to keep the magnitude of the current inversely proportional tothe number of melted tabs. At this point each of the elements isattached to its respective pin and the manufacturing ensemble can bedismantled. The module comprised of the glass substrate 9 pins 8, 8 and8" and elements 6, 6' and 6" is now ready for assembly with the spacer10 and anode l1.

Variations of the above mass production process are anticipated and theparameters, such as separation and/or pres sure between pins 23, 24 and25, elements 6, 6 and 6" and pins 8, 8, and 8" before and afterapplication of current, will have to be finalized through productionruns. Additional modifications of the above de-weld operation andcurrent are anticipated and the methods described areonly exemplary.

The method of the instant invention easily lends itself to a variety ofgas tube configurations. One of these configurations may be to have boththe anode and the cathode of the gas tube within the same plane. In thisembodiment, the discard pieces within the sheet or portions thereof willconstitute the anode and may be affixed to additional pins as discussedin respect to the cathode elements. After the anode pieces are affixed,they may be segregated from the sheet and/or the cathode elements by oneof the disclosed methods of buming off the connection tabs. The bum offmay be prior to, simultaneous with, or subsequent to the bum-off" of thecathode elements.

Test results indicate that the process for element fabrication andconnection can be reduced by the instant method without using massproduction techniques to one hour from four hours for the vacuum depositmethod. The advantageous results are due to the relative simplicity ofspot welding and segregating the pre-aligned elements in the segmentedplanar raised cathode electrode form of gas tube compared to the verytedious alignment, special handling precautions, and small quantity ofvacuum deposit batches possible in the vacuum deposited cathode form ofgas tubes.

While the above discussion has related to methods of electricallywelding and de-welding the elements of the pins, the invention is notintended to be limited to those methods. Any other methods of bondingand segregating such as direct heat application, using a laser beam,applying sonic means, or by chemical reactions are anticipated.

While the invention has been described in its preferred embodiment, itis to be understood that the words which have been used are words ofdescription rather than limitation and that changes within the previewof the appended claims may be made without departing from the true scopeand spirit of the invention in its broader scope.

I claim:

1. A method for fabricating a cathode array and base assembly of an gasdischarge type display tube comprising the steps of providing asubstantially planar non-conductive tube base having electricallyconductive cathode support pins passing in hermetically sealed relationthrough the base and extending upward from at least one surface thereof,providing a stencil-like electrically conductive sheet having cathodesegments formed therein in a predetermined pattern, the outline of saidsegments being formed by removal of sheet material around the peripheryof the segments except at discrete locations where small crosssectionalarea segments of the sheet material form tabs connecting the segments tothe sheet so as to support the segments in the'plane of the sheet,

placing the'stencil-like sheet in registered superposed relation withthe tube base so that a single point of each cathode segment ispositioned adjacent an extending end of a mating support pin with thesheet and tabs holding the undersurface of the segments in a commonplane closely above the tube base,

bonding each cathode segment to a mating support pin at the single pointof the individual segments adjacent the respective support pins toestablish a mechanically rigid electrical connection therebetween suchthat the cathode segments will remain substantially in said common planeupon being disconnected from the stencil sheet,

melting the tabs to sever the cathode segments from the remainingportion of the sheet to be discarded, and removing the portion of thesheet to be discarded.

2. A method for fabricating a cathode array and base assembly of analpha-numeric gas discharge tube comprising the steps of I providing asubstantially planar non-conductive tube base having electricallyconductive cathode support pins passing in hermetically sealed relationthrough the base and extending u ward from at least one surface thereof,providing a stenc -like electrically conductive sheet having cathodesegments formed therein in a predetermined pattern, the outline of saidsegments being formed by removal of sheet material around the peripheryof the segments except at discrete locations where small crosssectionalarea segments of the sheet material form tabs connecting the segments tothe sheet so as to support the segments in the plane of the sheet,

placing the stencil-like sheet in registered superposed relation withthe tube base so that a single point of each cathode segment is slightlyspaced above an extending end of a mating support pin in non-contactingrelation therewith, the sheet and tabs thereby holding the undersurfaceof the segments in a common plane above the tube base,

applying an electrical potential across each segment and mating supportpin while simultaneously exerting pressure on the segment to move itinto. contact with the mating pin to effect a weld therebetween forsecuring the segments to the respective pins with resulting tensionexerted on the tabs,

applying an electric potential across each cathode segment and theremaining portion of the sheet to be discarded to melt the tabs wherebyaffirmative disconnect is affected between the segments and sheets as aconsequence of the tension exerted on the tabs, and

removing the portion of the sheet to be discarded.

l *l l i i

1. A method for fabricating a cathode array and base assembly of an gasdischarge type display tube comprising the steps of providing asubstantially planar non-conductive tube base having electricallyconductive cathode support pins passing in hermetically sealed relationthrough the base and extending upward from at least one surface thereof,providing a stencil-like electrically conductive sheet having cathodesegments formed therein in a predetermined pattern, the outline of saidsegments being formed by removal of sheet material around the peripheryof the segments except at discrete locations where small cross-sectionalarea segments of the sheet material form tabs connecting the segments tothe sheet so as to support the segments in the plane of the sheet,placing the stencil-like sheet in registered superposed relation withthe tube base so that a single point of each cathode segment ispositioned adjacent an extending end of a mating support pin with thesheet and tabs holding the undersurface of the segments in a commonplane closely above the tube base, bonding each cathode segment to amating support pin at the single point of the individual segmentsadjacent the respective support pins to establish a mechanically rigidelectrical connection therebetween such that the cathode segments willremain substantially in said common plane upon being disconnected fromthe stencil sheet, melting the tabs to sever the cathode segments fromthe remaining portion of the sheet to be discarded, and removing theportion of the sheet to be discarded.
 2. A method for fabricating acathode array and base assembly of an alpha-numeric gas discharge tubecomprising the steps of providing a substantially planar non-conductivetube base having electrically conductive cathode support pins passing inhermetically sealed relation through the base and extending upward fromat least one surface thereof, providing a stencil-like electricallyconductive sheet having cathode segments formed therein in apredetermined pattern, the outline of said segments being formed byremoval of sheet material around the periphery of the segments except atdiscrete locations where small cross-sectional area segments of thesheet material form tabs connecting the segments to the sheet so as tosupport the segments in the plane of the sheet, placing the stencil-likesheet in registered superposed relation with the tube base so that asingle point of each cathode segment is slightly spaced above anextending end of a mating support pin in non-contacting relationtherewith, the sheet and tabs thereby holding the undersurface of thesegments in a common plane above the tube base, applying an electricalpotential across each segment and mating support pin whilesimultaneously exerting pressure on the segment to move it into contactwith the mating pin to effect a weld therebetween for securing thesegments to the respective pins with resulting tension exerted on thetabs, applying an electric potential across each cathode segment and theremaining portion of the sheet to be discarded to melt the tabs wherebyaffirmative disconnect is affected between the segments and sheets as aconsequence of the tension exerted on the tabs, and removing the portionof the sheet to be discarded.